Polytetrafluoroethylene pipe with high impact resistance and method for manufacturing the same

Abstract

The present application relates to a kind of polytetrafluoroethylene pipe with high impact resistance and its preparation method.The pipe includes polytetrafluoroethylene resin matrix and distributed perfluoroalkoxy resin, polyimide micro powder, acicular calcium silicate and graphite fluoride.The above-mentioned solid components are mixed step by step during preparation, and are wetted by extrusion aid, twice cold-pressed, de-extrusion aid and sectional sintering, while the relative density of two-stage solid skeleton and its multiple relationship are controlled with the theoretical volume of solid components after de-extrusion aid as the unified calculation reference.The present application is beneficial to improve the structural integrity of pipe wall, dimensional stability and impact resistance.

Description

Technical Field

[0001] This invention relates to the technical field of polytetrafluoroethylene (PTFE) pipes, and in particular to a PTFE pipe with high impact resistance and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) possesses excellent chemical corrosion resistance, heat resistance, weather resistance, and low friction properties, making it widely used in chemical transportation, semiconductor cleaning, medical equipment, electronic and electrical insulation, and the transportation of high-purity fluids. PTFE pipes are typically used in environments involving corrosive media, alternating high and low temperatures, pressure fluctuations, or assembly impacts. Therefore, in addition to corrosion resistance and temperature resistance, their impact resistance and pipe wall structure stability directly affect the reliability of the pipes.

[0003] Existing polytetrafluoroethylene (PTFE) pipes are mostly manufactured through processes such as powder molding, additive removal, and sintering. Due to the high melt viscosity and poor melt flow of PTFE, the pipe wall structure is mainly formed by the compaction and sintering of powder particles during the molding process. If the powder accumulation, compaction of the compacted blank, additive removal, and sintering shrinkage are not adequately coordinated, local pores, loose interfaces, or areas of residual stress concentration can easily form inside the pipe wall. This can cause crack propagation, end cracking, or localized damage when the pipe is subjected to external impact, installation compression, or temperature changes.

[0004] To improve the mechanical properties of PTFE pipes, a certain amount of reinforcing fillers or modified resins are typically added to the PTFE resin to enhance the material's rigidity, wear resistance, or dimensional retention. However, the interfacial bonding state between PTFE and different fillers, the dispersion state of the fillers during powder molding, and the continuity of the pipe wall after sintering all affect the final pipe performance. If only the type or amount of filler is considered, a mismatch between increased rigidity and maintained toughness can easily occur. Especially when the pipe is subjected to impact loads, local interfacial defects and stress concentrations at the filler ends can still become crack initiation sites.

[0005] Therefore, how to improve the structural stability of PTFE pipes under impact loads and reduce local defects in the pipe wall caused by the molding and sintering process while maintaining the inherent properties of PTFE pipes such as corrosion resistance, temperature resistance and low friction is a technical problem that needs to be solved in the field of PTFE pipes. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a polytetrafluoroethylene (PTFE) pipe with high impact resistance and its preparation method. While maintaining the corrosion resistance, temperature resistance and low friction performance of PTFE pipe, it improves the structural stability of the pipe when subjected to impact and reduces local cracking and impact damage of the pipe wall.

[0007] To achieve the above objectives, the first aspect of the present invention provides a polytetrafluoroethylene (PTFE) pipe with high impact resistance, the PTFE pipe comprising a PTFE resin matrix and perfluoroalkoxy resin, polyimide micro powder, needle-shaped calcium silicate, and fluorinated graphite distributed in the PTFE resin matrix. Based on 100 parts by weight of the polytetrafluoroethylene resin matrix, the perfluoroalkoxy resin comprises 4 to 8 parts by weight, the polyimide micro powder comprises 2.5 to 6 parts by weight, the needle-shaped calcium silicate comprises 7 to 13 parts by weight, and the fluorinated graphite comprises 0.6 to 1.6 parts by weight. The mass ratio of the perfluoroalkoxy resin to the polyimide micro powder is 1.0 to 2.2:1, the mass ratio of the polyimide micro powder to the needle-shaped calcium silicate is 1:1.8 to 3.8, and the mass ratio of the fluorinated graphite to the needle-shaped calcium silicate is 1:6 to 18.

[0008] By using polytetrafluoroethylene resin as the main material and simultaneously introducing perfluoroalkoxy resin, polyimide micro powder, needle-shaped calcium silicate and fluorinated graphite, a composite impact-resistant system is formed inside the pipe, which consists of a fluorinated resin auxiliary binding phase, a heat-resistant micro powder dispersion phase, a needle-shaped load-bearing phase and a sheet-like low-shear phase.

[0009] The perfluoroalkoxy resin and polytetrafluoroethylene (PTFE) resin exhibit good fluorine compatibility, which helps improve the interfacial bonding between the main resin particles and around the filler during heat treatment, and provides a more stable embedding environment for polyimide micropowder and needle-like calcium silicate. The polyimide micropowder, distributed in the resin bonding area and around the needle-like calcium silicate, forms stress transition and dispersion nodes under impact loads, making the load transfer path formed by the needle-like calcium silicate smoother. Fluorinated graphite, relying on its flake-like low-shear properties, forms an interface conditioning region between the needle-like calcium silicate and the fluorinated resin phase, allowing for the appropriate release of local slippage and micro-deformation generated during impact. Thus, impact energy can be progressively transferred and dissipated between the resin fusion region, the polyimide micropowder dispersion region, the needle-like calcium silicate load-bearing path, and the fluorinated graphite conditioning interface, enabling rigidity enhancement, toughness compensation, and interface stability to be interconnected within the same composite system. This improves the impact resistance of PTFE pipes and reduces the risk of brittle cracking in filler-reinforced systems.

[0010] Furthermore, in the powder compounding, extrusion aid wetting, cold pressing embedding, extrusion aid removal and sintering process of polytetrafluoroethylene (PTFE) pipes, the PTFE main resin does not rely on sufficient melt flow to achieve the re-homogenization of each filler. The final stress state of the filler is mainly determined by the initial powder dispersion, compact embedding, interface relaxation after extrusion aid removal, and subsequent sintering. Therefore, controlling the mass ratio of perfluoroalkoxy resin to polyimide micropowder to 1.0–2.2:1 ensures a suitable wetting and embedding environment for the polyimide micropowder, allowing it to participate more stably in impact load dispersion. Controlling the mass ratio of polyimide micropowder to needle-shaped calcium silicate to 1:1.8–3.8 allows the point-like stress dispersion nodes formed by the micropowder to connect with the linear load-bearing path formed by the needle-shaped calcium silicate, resulting in a smoother transition when the load is transferred from the main resin to the needle-shaped filler. Controlling the mass ratio of fluorinated graphite to needle-shaped calcium silicate to 1:6–18 allows the low-shear effect of fluorinated graphite to focus on the interface release around the needle-shaped calcium silicate, both mitigating the concentrated stress at the rigid filler interface and maintaining the overall continuity of the pressed compact and sintered tubing.

[0011] Therefore, the aforementioned proportional relationship, in conjunction with the molding process of this type of PTFE pipe, corresponds to three consecutive levels: micro-powder embedding, point-line stress connection, and interface micro-slip release. This allows the multiphase components to form an orderly coordination around the dispersion, transmission, and dissipation of impact loads. This structure enables the pipe to achieve more stable impact resistance while maintaining the corrosion resistance, temperature resistance, and low friction characteristics of PTFE material, and also takes into account the compaction stability during the molding process and the structural integrity after sintering.

[0012] Preferably, the polytetrafluoroethylene resin includes a first-size polytetrafluoroethylene resin and a second-size polytetrafluoroethylene resin, wherein the average particle size of the first-size polytetrafluoroethylene resin is 25-45 μm, the average particle size of the second-size polytetrafluoroethylene resin is 50-75 μm, and the mass ratio of the first-size polytetrafluoroethylene resin to the second-size polytetrafluoroethylene resin is 1:1.2-3.0.

[0013] By setting the polytetrafluoroethylene (PTFE) resin as a combination of PTFE resin with a first particle size and PTFE resin with a second particle size, and limiting their average particle size and mass ratio, the main resin forms a coarse-fine particle synergistic packing structure during powder mixing, extrusion aid wetting, cold pressing, and sintering. The PTFE resin with the first particle size can fill the gaps between the particles of the PTFE resin with the second particle size, improving the packing density of the powder system and providing a more uniform embedding space for finer components such as perfluoroalkoxy resin, polyimide micropowder, and fluorinated graphite; the PTFE resin with the second particle size forms a more stable main skeleton, enabling the wetted powder to have better compaction response and shape retention during the cold pressing stage.

[0014] Preferably, the average particle size of the perfluoroalkoxy resin is 8–25 μm, the average particle size D50 of the polyimide micropowder is 2–6 μm, and the ratio of the average particle size of the perfluoroalkoxy resin to the average particle size D50 of the polyimide micropowder is 2.0–7.5:1; the average particle size D50 of the fluorinated graphite is 3–9 μm, the ratio of the average particle size D50 of the fluorinated graphite to the average particle size D50 of the polyimide micropowder is 0.8–2.5:1, and the mass ratio of the fluorinated graphite to the needle-shaped calcium silicate is 1:7–16.

[0015] The average particle size of the perfluoroalkoxy resin is controlled at 8–25 μm, and the average particle size D50 of the polyimide micropowder is controlled at 2–6 μm. The ratio of the average particle size of the perfluoroalkoxy resin to the average particle size D50 of the polyimide micropowder is 2.0–7.5:1, which allows the perfluoroalkoxy resin to form a relatively stable fluorinated wetting and embedding region around the polyimide micropowder. This particle size ratio makes it easier for the polyimide micropowder to enter the bonding region formed by the perfluoroalkoxy resin and polytetrafluoroethylene resin. During subsequent cold pressing and sintering, it is less likely to concentrate in the interpowder gaps as isolated fine powder, thus enabling the polyimide micropowder to more stably form fine-scale stress dispersion nodes under impact loads.

[0016] The average particle size D50 of fluorinated graphite is controlled to be 3–9 μm, and the ratio of the average particle size D50 of fluorinated graphite to that of polyimide micropowder is 0.8–2.5:1, which ensures that fluorinated graphite and polyimide micropowder are spatially similar. They are more likely to form an adjacent distribution relationship around the needle-like calcium silicate, allowing the point stress transition provided by the polyimide micropowder and the sheet-like low-shear release provided by the fluorinated graphite to act on the same local interface region. Thus, when impact loads are transferred to the vicinity of the needle-like calcium silicate, the local stress can first be dispersed by the polyimide micropowder, and then the micro-slip stress at the needle-like filler interface can be mitigated by the fluorinated graphite, reducing the spatial disconnect between the point-like dispersion region and the sheet-like release region.

[0017] Based on the aforementioned particle size ratio, the mass ratio of fluorinated graphite to acicular calcium silicate is further limited to 1:7–16, ensuring that the low-shear interface regulation effect of fluorinated graphite corresponds to the rigid load-bearing path of acicular calcium silicate. This mass ratio allows fluorinated graphite to primarily function around the local interfaces near the ends and sidewalls of the acicular calcium silicate, providing limited space for the release of concentrated stress generated when the acicular calcium silicate is impacted. Simultaneously, the amount of fluorinated graphite used does not create too many independent lubrication interfaces, which is beneficial for maintaining the compactness of the compact and the continuous structure of the tube wall after sintering. Therefore, micro-powder stress dispersion nodes and low-shear release interfaces can be simultaneously formed around the acicular calcium silicate, allowing the linear load-bearing path to participate more stably in the transfer and dissipation of impact energy within the tube.

[0018] Preferably, the needle-shaped calcium silicate has an average length of 10–28 μm, an average diameter of 0.6–2.2 μm, an aspect ratio of 8–20, and the ratio of the average length of the needle-shaped calcium silicate to the average particle size of the perfluoroalkoxy resin is 0.7–2.6:1.

[0019] Needle-shaped calcium silicate, with an average length of 10–28 μm, an average diameter of 0.6–2.2 μm, and an aspect ratio of 8–20, is advantageous for forming a short-range linear load-bearing structure within PTFE tubing, allowing impact loads to be dispersed and deflected within the tubing wall. Its key function lies in utilizing the needle-like morphology to provide a directional force transmission path, while avoiding excessively large sizes that could significantly interfere with powder mixing, cold pressing, and sintering continuity.

[0020] The ratio of the average length of the needle-shaped calcium silicate to the average particle size of the perfluoroalkoxy resin is further limited to 0.7–2.6:1, thus matching the linear load-bearing scale of the needle-shaped calcium silicate with the fusion bonding scale of the perfluoroalkoxy resin. Under this scalar relationship, the perfluoroalkoxy resin can provide a fluorinated resin-assisted bonding environment around the needle-shaped calcium silicate during sintering, making it less likely for the needle-shaped calcium silicate to be distributed as an isolated rigid filler in the polytetrafluoroethylene matrix, but rather easier to form a smoother interfacial transition structure with the surrounding fluorinated resin phase. When impact loads are transmitted to the vicinity of the needle-shaped calcium silicate, they can first be buffered by the fluorinated interfacial transition region formed by the perfluoroalkoxy resin, and then the needle-shaped calcium silicate bears the linear transmission and crack deflection effects, thereby making the stress connection between the rigid load-bearing structure and the resin matrix smoother.

[0021] This sizing relationship also aligns with the particle size ratio of the aforementioned polyimide micropowder and fluorinated graphite, ensuring that the area surrounding the needle-like calcium silicate simultaneously possesses fusion bonding, micropowder dispersion, and low-shear release conditions. In this way, the linear load-bearing capacity of the needle-like calcium silicate can be stably incorporated into the continuous phase of the fluorinated resin, making the load transfer path more continuous when the pipe is subjected to impact, making it easier to disperse and release localized stress concentrations, while also considering the stability of the pressed blank, the continuity of the pipe wall after sintering, and impact resistance.

[0022] Preferably, the surface of the needle-shaped calcium silicate has a fluorinated silane treatment layer, which is formed by hydrolysis and condensation treatment of one of perfluorooctyltriethoxysilane, tridecafluorooctyltriethoxysilane or trifluoropropyltrimethoxysilane, and the wetting contact angle of the needle-shaped calcium silicate powder after fluorinated silane treatment is 95° to 125°.

[0023] After a fluorinated silane treatment layer is formed on the surface of needle-shaped calcium silicate, a more suitable interface state for multi-phase synergistic stress can be formed in the composite impact-resistant system of the present invention. The needle-shaped calcium silicate is simultaneously within the fusion bonding range of the perfluoroalkoxy resin, the stress transition range of the polyimide micropowder, and the low-shear modulation range of the fluorinated graphite. Its surface state affects whether the above effects can form a continuous coordination around the needle-shaped load-bearing phase. The fluorinated silane treatment layer can transform the surface of the needle-shaped calcium silicate from a directly rigid interface to a transitional interface more suitable for the embedding of the fluorinated resin phase. This makes it easier for the perfluoroalkoxy resin to participate in the interface transition around the needle-shaped calcium silicate during sintering, while providing a stable boundary for the fluorinated graphite to exert a limited micro-slip release effect near the needle-shaped filler.

[0024] The contact angle of acicular calcium silicate treated with a fluorinated silane layer is controlled to be 95°–125°, ensuring that its surface is in a state of moderate fluorination and moderate interfacial restraint. This contact angle range complements the linear load-bearing effect of acicular calcium silicate, the fusion bonding effect of perfluoroalkoxy resin, and the low-shear release effect of fluorinated graphite in this invention. This allows the acicular calcium silicate to be stably embedded in the fluorinated continuous phase formed by polytetrafluoroethylene resin and perfluoroalkoxy resin without weakening its load-bearing embedding state due to excessive low-friction at the interface. In this way, an interfacial environment with fusion bonding, stress transition, and controlled release can be formed around the acicular calcium silicate, enabling it to more stably bear the linear load transfer and crack deflection under impact loads, and reducing the risk of local crack initiation at the ends and sidewalls.

[0025] A second aspect of the present invention provides a method for preparing the polytetrafluoroethylene (PTFE) tubing as described above, comprising the following steps: S1: Mix perfluoroalkoxy resin, polyimide micro powder and the first part of polytetrafluoroethylene resin to obtain a pre-dispersed powder; S2: Add the second part of polytetrafluoroethylene resin, needle-shaped calcium silicate and fluorinated graphite to the pre-dispersed powder and mix to obtain composite powder; S3: Add the hydrocarbon liquid extrusion aid to the composite powder by spraying, seal and let stand to obtain wet powder; S4: The wet powder is loaded into the tube blank mold for the first cold pressing to obtain the first blank. After the pressure is released and the first blank is allowed to stand, the first blank is cold pressed a second time to obtain the second blank. S5: The secondary pressed billet is subjected to a de-extrusion agent treatment to obtain a de-extrusion agent tube blank; S6: The de-additive tube blank is subjected to pre-sintering, main sintering, heat preservation and cooling shaping in sequence to obtain polytetrafluoroethylene tubes; Using the theoretical volume of the solid components after removing hydrocarbon liquid extrusion aids as a unified calculation benchmark, the relative density of the solid skeleton generated after the first cold pressing and subsequent depressurization and static setting of the primary compact is 2.0%–5.5%; the relative density of the solid skeleton generated after the second cold pressing and subsequent extrusion aid removal of the secondary compact is 1.0%–3.5%. The relative density of the solid skeleton produced after the first cold pressing and subsequent static setting is 2 to 4 times that of the solid skeleton produced after the second cold pressing and subsequent treatment with the extrusion aid removal agent.

[0026] By employing the above preparation method, the perfluoroalkoxy resin, polyimide micropowder, and the first part of polytetrafluoroethylene resin are first pre-dispersed, and then the second part of polytetrafluoroethylene resin, needle-shaped calcium silicate, and fluorinated graphite are added for secondary mixing. This allows the fluorinated fusion component and the micropowder stress-dispersing component to first form a basic embedded state in a portion of the polytetrafluoroethylene resin, and then the needle-shaped calcium silicate and fluorinated graphite are introduced into this basic dispersion system. This reduces the local enrichment that occurs when fine powder, needle-shaped fillers, and flake fillers are directly mixed. This stepwise mixing method, combined with the subsequent two cold pressing molding processes, allows the fluorinated interface bonding area, micropowder stress-dispersing nodes, needle-shaped load-bearing paths, and low-shear release interfaces to be gradually fixed in the tube blank, providing a foundation for the formation of a stable impact-resistant structure after sintering.

[0027] The control of the relative density reduction rate of the solid skeleton after the first cold pressing and subsequent depressurization and settling is 2.0% to 5.5% reflects that the solid skeleton of the wet powder still retains a moderate amount of structural release space after the initial compaction. This reduction in relative density does not simply indicate a loose compact, but rather represents the limited geometric rebound of the solid skeleton caused by stress relaxation and local positional adjustment after the first high-pressure embedding of polytetrafluoroethylene powder, extrusion aids, and various fillers. For the composite powder system of this invention, which simultaneously contains polyimide micropowder, needle-shaped calcium silicate, and fluorinated graphite, if the goal is to prevent a reduction in solid skeleton density after the initial cold pressing, high local compressive stress is likely to remain at the ends of the needle-shaped calcium silicate, in areas where polyimide micropowder is concentrated, and around the fluorinated graphite flakes. By controlling the moderate reduction in relative density of the solid skeleton after depressurization and settling of the first compact, these locally stressed areas can experience limited release first, preventing them from concentrating into abrupt changes in porosity or interfacial cracks during subsequent extrusion aid removal and sintering.

[0028] Furthermore, controlling the relative density decline rate of the solid skeleton generated after the second cold pressing and subsequent treatment with extrusion aid removal to 1.0%–3.5% reflects the good geometric stability, particle embedding, and interface support capacity of the tube blank after the extrusion aid is removed. This decline in relative density mainly corresponds to the evaporation and removal of the extrusion aid, the reduction of wetting medium between powders, and the retention of the structure after pore redistribution. It does not indicate that the main resin sintering shrinkage occurs during the extrusion aid removal stage. Because fluorinated graphite has low shear characteristics, needle-like calcium silicate has a rigid linear structure, and polyimide micropowder is distributed in local gaps, a large decline in the relative density of the solid skeleton after extrusion aid removal easily indicates that the filler embedding relationship formed in the early stage has not been stably retained. Controlling this decline rate within a low range allows the particle contact and filler embedding relationship re-established during the second cold pressing to be maintained after extrusion aid removal, thus making it easier to form continuous resin fusion and a stable filler interface in the subsequent sintering stage.

[0029] More importantly, the relative density reduction rate of the solid skeleton generated after the first cold pressing and subsequent static settling is controlled to be 2 to 4 times that of the solid skeleton generated after the second cold pressing and subsequent removal of the extrusion aid. This difference in relative density reduction between the two stages serves as an adjustment condition for the release and retention of the internal structure of the tube blank. This ratio allows for graded control of the release space after the first cold pressing and the retainable space after the second cold pressing. The higher relative density reduction rate of the solid skeleton after the first cold pressing ensures that the wet composite powder still has appropriate stress relaxation and local rearrangement margin after the initial compaction, which is used to release the uneven internal stress caused by the extrusion of needle-shaped calcium silicate ends, the local aggregation of polyimide micropowder, and the slippage of fluorinated graphite flakes. The lower relative density reduction rate of the solid skeleton after the second cold pressing and removal of the extrusion aid limits the pore expansion and interface relaxation after the extrusion aid is discharged, allowing the filler embedding relationship released in the early stage to be recompacted and stably retained. When the two maintain a 2 to 4-fold relationship, the former stage undertakes the active release and rearrangement function, while the latter stage undertakes the skeleton maintenance and interface fixation function, thereby enabling the tube blank to smoothly transition from a wet and compacted state to a stable sintering state after the additives are removed.

[0030] Preferably, the hydrocarbon liquid extrusion aid is selected from one of isoparaffin solvent oil, naphtha, and white oil. The initial boiling point of the hydrocarbon liquid extrusion aid is 150–220°C, the final boiling point is 230–320°C, and the kinematic viscosity at 40°C is 1.0–5.0 mm. 2 / s.

[0031] The initial boiling point of the hydrocarbon liquid extrusion aid is controlled at 150–220℃, the final boiling point is controlled at 230–320℃, and the kinematic viscosity at 40℃ is controlled at 1.0–5.0 mm. 2The additive, with a particle size distribution of 600 μm, is compatible with the powder system composed of coarse and fine-grained polytetrafluoroethylene resin, perfluoroalkoxy resin, polyimide micropowder, needle-shaped calcium silicate, and fluorinated graphite in this invention. This allows the extrusion aid to maintain good penetration, wetting, and particle slip regulation during the mixing and cold pressing stages, promoting the uniform embedding of fine powder components and needle-shaped fillers in the main resin. Simultaneously, it can be discharged more smoothly during the subsequent extrusion aid removal process, reducing abrupt changes in porosity and interfacial loosening caused by localized rapid volatilization. Therefore, the wetted powder can form a more stable compacted structure during the cold pressing stage, and the porosity change of the tube blank after extrusion aid removal is more gradual, providing a foundation for the continuous sintering and fusion and the stable formation of impact-resistant stress paths.

[0032] Preferably, in step S1, the first part of polytetrafluoroethylene resin accounts for 28% to 42% of the total mass of polytetrafluoroethylene resin; the perfluoroalkoxy resin, polyimide micro powder and the first part of polytetrafluoroethylene resin are mixed at 80 to 160 r / min for 10 to 16 min.

[0033] Through the above control, a moderately open fine powder embedding environment can be formed in the pre-dispersion stage. When the amount of polytetrafluoroethylene resin in the first part is within this range, it can provide sufficient space for the attachment and embedding of the main resin and polyimide microparticles, without weakening the effect of the second part of polytetrafluoroethylene resin in forming a skeleton due to excessive addition of the main resin at one time. In this way, the perfluoroalkoxy resin can first form a fluorinated bonding base around the polyimide microparticles and some polytetrafluoroethylene particles, and the polyimide microparticles can also enter the local gaps of the main resin relatively uniformly, providing pre-dispersion conditions for the stress transition and interface release structure formed after the subsequent addition of needle-shaped calcium silicate and fluorinated graphite.

[0034] The pre-dispersion speed is controlled at 80–160 r / min, and the time is controlled at 10–16 min. This matches the particle size of the perfluoroalkoxy resin and polyimide micropowder, allowing the fine powder components to be dispersed and embedded under relatively mild shear. These mixing conditions help reduce polyimide micropowder agglomeration and avoid excessive shear that could cause unfavorable fibrosis in the polytetrafluoroethylene powder or make the subsequent powder packing unstable. As a result, the pre-dispersed powder has formed a relatively stable fluorinated resin coating and micropowder dispersion base before entering the secondary mixing stage. This makes it easier to control the relative density of the solid skeleton in subsequent cold pressing, maintain the structure after removing the extrusion aid, and achieve continuous fusion in the sintering stage.

[0035] Preferably, in step S4, the pressure of the first cold pressing is 18-28 MPa, and the holding time is 3-8 min; the pressure release and standing time is 12-35 min; the pressure of the second cold pressing is 24-38 MPa, and the holding time is 5-12 min.

[0036] By controlling the pressure and holding time of the first cold pressing in step S4, the composite powder moistened by the extrusion aid can first form a preliminary compacted state and filler embedding. This stage does not directly pursue final densification, but rather allows the coarse and fine-sized polytetrafluoroethylene resin, perfluoroalkoxy resin, polyimide micro powder, needle-shaped calcium silicate, and fluorinated graphite to complete their initial contact, sliding, and alignment under moist conditions, thus preserving adequate structural adjustment space within the powder for subsequent pressure relief and settling.

[0037] Secondly, the depressurization and settling time is controlled to be 12–35 minutes, which allows the primary compaction to complete limited elastic recovery, redistribution of extrusion aids, and relaxation of the filler interface after the initial compaction. This process is connected with the aforementioned control of the relative density reduction rate of the solid skeleton, so that the local extrusion stress near the ends and sidewalls of the needle-shaped calcium silicate, the packing stress around the polyimide micropowder, and the slip stress near the fluorinated graphite flakes are appropriately released, creating conditions for the second cold pressing to re-establish a stable intercalation relationship.

[0038] Finally, the second cold pressing pressure is controlled at 24–38 MPa, and the holding time is controlled at 5–12 minutes. This allows for re-compacting and structural fixation of the tube blank, based on the local relaxation and position adjustment already completed in the previous stage. Because the second cold pressing pressure and holding time are higher than the first cold pressing stage, it further improves the particle contact tightness and filler embedding stability, resulting in a more stable and dense skeleton in the tube blank before the extrusion aid is discharged. Thus, a continuous forming process is formed between the first cold pressing, depressurization and settling, and the second cold pressing, involving initial embedding, release and adjustment, and then densification and fixation. This prevents abrupt changes in porosity, interface loosening, and local cracking in the tube blank during subsequent extrusion aid removal and sintering, and helps maintain the structural integrity and impact resistance of the tube wall after sintering.

[0039] Preferably, in step S6, the pre-sintering temperature is 305–325℃, and the pre-sintering time is 25–45 min; the main sintering temperature is 368–382℃, and the main sintering time is 45–85 min; the holding temperature is 352–365℃, and the holding time is 25–55 min; during the cooling and shaping process, the average cooling rate from the main sintering temperature to 260℃ is 0.8–2.2℃ / min, and the average cooling rate from 260℃ to 180℃ is 0.4–1.3℃ / min.

[0040] First, in step S6, the pre-sintering temperature is controlled at 305–325℃ and the pre-sintering time is controlled at 25–45 min. This allows the de-additive-treated billet to undergo a relatively gradual thermal response adjustment before entering the main sintering stage. This stage is beneficial for further releasing the residual local internal stress after de-additive removal and for gradually stabilizing the contact interfaces between polytetrafluoroethylene resin, perfluoroalkoxy resin, and various fillers, reducing pore expansion or interface disturbance caused by sudden temperature changes when directly entering the high-temperature sintering stage.

[0041] Secondly, controlling the main sintering temperature to 368–382℃ and the main sintering time to 45–85 min allows for sufficient sintering bonding of the polytetrafluoroethylene (PTFE) main resin, and enables the perfluoroalkoxy resin to play an auxiliary fusion role around the PTFE particles, polyimide micropowder, and needle-like calcium silicate. This temperature and time range aligns with the structural retention state after powder dispersion, cold pressing, and additive removal, allowing the fluorine-containing interfacial bonding region to form a continuous connection along the multiphase interface, thereby improving the overall density of the pipe wall and the stability of the filler embedding.

[0042] Furthermore, controlling the holding temperature to 352–365℃ and the holding time to 25–55 minutes further stabilizes the internal fusion structure of the tube blank after the main sintering, allowing for a more balanced thermal setting of the polytetrafluoroethylene main phase, the perfluoroalkoxy resin-assisted fusion region, and the interface surrounding the needle-like calcium silicate. This process helps reduce the residual stress formed by the inconsistent structural shrinkage between the inner and outer layers of the tube wall before cooling after sintering, ensuring good continuity of the aforementioned impact-resistant stress path after sintering.

[0043] Finally, during the cooling and shaping process, the average cooling rate from the main sintering temperature to 260℃ is 0.8–2.2℃ / min, and the average cooling rate from 260℃ to 180℃ is 0.4–1.3℃ / min. This allows the pipe to gradually shrink and solidify as it transitions from a high-temperature fused structure to a stable solid structure. The first cooling stage primarily controls the crystallization and volume shrinkage rhythm of the polytetrafluoroethylene (PTFE) main phase and the fluorinated interface bonding region. The second cooling stage further mitigates the release of residual stress inside the pipe wall, preventing the formation of new microcracks or interface loosening at the interfaces containing needle-like calcium silicate, polyimide micropowder, and fluorinated graphite due to differences in cooling shrinkage.

[0044] Therefore, the combined action of pre-sintering, main sintering, heat preservation, and segmented cooling enables the tube blank after additive removal to complete fusion, shaping, and stress balancing in a relatively stable thermal process, thereby improving the integrity of the tube wall, dimensional stability, and impact resistance after sintering.

[0045] The present invention, by adopting the above technical solution, has the following beneficial effects: (1) This invention uses polytetrafluoroethylene resin as the main body, and through the combination of perfluoroalkoxy resin, polyimide micro powder, needle-shaped calcium silicate and fluorinated graphite, a composite impact-resistant structure is formed inside the pipe, which is connected by fluorine-containing fusion, micro powder stress dispersion, needle-shaped linear load bearing and low shear interface release. Perfluoroalkoxy resin provides a more continuous fluorine-containing intercalation environment for polyimide micro powder and needle-shaped calcium silicate. Polyimide micro powder provides transitional dispersion of local stress around needle-shaped calcium silicate. Fluorinated graphite provides limited micro-slip release around needle-shaped calcium silicate, so that the impact load can be dispersed, transmitted and dissipated step by step inside the pipe wall, thereby improving the impact resistance stability of polytetrafluoroethylene pipe and reducing the risk of local cracking and brittle cracking after the introduction of rigid filler.

[0046] (2) This invention limits the composition ratio, particle size ratio, and scale ratio to create a stress-matching relationship between the phases suitable for the cold-pressed sintering system of polytetrafluoroethylene powder. The ratio of perfluoroalkoxy resin to polyimide micropowder provides a suitable fluorinated wetting and embedding environment for the micropowder; the ratio of polyimide micropowder to needle-shaped calcium silicate connects the point stress dispersion nodes with the linear load-bearing path; and the ratio of fluorinated graphite to needle-shaped calcium silicate ensures that low-shear release mainly functions around the needle-shaped rigid interface. Simultaneously, the particle size and scale relationships among the perfluoroalkoxy resin, polyimide micropowder, fluorinated graphite, and needle-shaped calcium silicate further enhance the spatial coordination between micropowder embedding, interface transition, and needle-shaped load bearing. Therefore, the reinforcing phase inside the pipe is not simply dispersed in the main resin, but forms a more continuous and smoother multi-level stress structure around the impact load transmission path.

[0047] (3) This invention employs a preparation process combining stepwise pre-dispersion, extrusion aid wetting, two-stage cold pressing, extrusion aid removal, and segmented sintering and shaping, enabling continuous control of the composite powder from dispersion and embedding to compaction and fixation, and finally to sintering and fusion. In particular, by controlling the relative density reduction rate of the solid skeleton generated after the first cold pressing and subsequent static setting, and the relative density reduction rate of the solid skeleton generated after the second cold pressing and subsequent extrusion aid removal, and making the former 2 to 4 times that of the latter, the tube blank has adequate stress release and position adjustment space after the initial compaction, and can maintain a relatively stable solid skeleton and filler embedding state after the second compaction and extrusion aid removal. This process helps to reduce abrupt changes in pore size, loose interfaces, and residual stress concentration during the extrusion aid removal and sintering stages, resulting in sintered tubes with good wall integrity, dimensional stability, and impact resistance. Detailed Implementation

[0048] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0049] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0050] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0051] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0052] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention. Example 1

[0053] This embodiment discloses a polytetrafluoroethylene (PTFE) pipe with high impact resistance. The raw materials for its preparation, by weight, include the following components: 100 parts of polytetrafluoroethylene resin; 6 parts of perfluoroalkoxy resin; 3.6 parts of polyimide micro powder; 9.5 parts of needle-shaped calcium silicate; 0.9 parts of fluorinated graphite; 23 parts of hydrocarbon liquid extrusion aid.

[0054] The polytetrafluoroethylene (PTFE) resin is composed of PTFE resin with a first particle size and PTFE resin with a second particle size. The PTFE resin with the first particle size is a suspension-processed PTFE molding powder with a standard specific gravity of 2.17, an average particle size of 35 μm, an apparent density of 450 g / L, and a dosage of 35 parts. The PTFE resin with the second particle size is also a suspension-processed PTFE molding powder with a standard specific gravity of 2.18, an average particle size of 62 μm, an apparent density of 520 g / L, and a dosage of 65 parts. The mass ratio of the PTFE resin with the first particle size to the PTFE resin with the second particle size is 1:1.86.

[0055] The perfluoroalkoxy resin is a melt-processable copolymer powder formed by tetrafluoroethylene and perfluoropropyl vinyl ether, wherein the molar content of the perfluoropropyl vinyl ether structural unit is 3.5%, the melting point is 305℃, the melt flow rate is 8g / 10min, the melt flow rate test conditions are 372℃ and 5kg, the average particle size is 15μm, and the apparent density is 420g / L.

[0056] The polyimide micro powder is a fully aromatic polyimide micro powder formed by polycondensation and thermal imidization of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether. The polymer backbone contains pyromellitic dianhydride structural units and diphenyl ether structural units. The thermal decomposition temperature is 535℃, the glass transition temperature is 315℃, the average particle size D50 is 4μm, the average D90 is 8μm, and the water content is 0.12%.

[0057] Fluorinated graphite is a layered fluorinated graphite powder with an average particle size D50 of 5 μm and a fluorine-to-carbon atomic ratio of 0.9:1.

[0058] Needle-shaped calcium silicate is needle-shaped wollastonite powder with an average length of 18 μm, an average diameter of 1.2 μm, and an aspect ratio of 15.

[0059] The surface of needle-shaped calcium silicate has a fluorinated silane-treated layer, which is formed by the hydrolysis and condensation of 1H,1H,2H,2H-tridecylfluorooctyltriethoxysilane. The treatment method for the fluorinated silane-treated layer on the surface of needle-shaped calcium silicate is as follows: 9.5 parts of needle-shaped calcium silicate are added to a treatment solution composed of anhydrous ethanol, deionized water, and 1H,1H,2H,2H-tridecylfluorooctyltriethoxysilane, with a mass ratio of 90:8:2. The pH of the treatment solution is adjusted to 4.5 with glacial acetic acid, and the solution is stirred at 45°C for 2 hours. After filtration, the solution is dried at 105°C for 3 hours to obtain fluorinated silane-treated needle-shaped calcium silicate. The drying temperature is used to promote the condensation and fixation between the silane hydrolysis products and the hydroxyl groups on the surface of the needle-shaped calcium silicate, and to remove free solvent; it is not used as a decomposition condition for the fluorinated alkyl segments.

[0060] The wetting contact angle of the treated needle-shaped calcium silicate powder was 110°. The powder wetting contact angle was determined using the Washburn capillary rise method. The treated needle-shaped calcium silicate powder was packed into a powder contact angle test sample tube to form a powder bed under the same packing mass and gentle vibration conditions. The capillary constant of the powder bed was calibrated with n-hexane, and deionized water was used as the test solution. The powder wetting contact angle was calculated according to the Washburn equation. The test temperature was 25℃, and each group of samples was tested in parallel three times, and the average value was taken.

[0061] The hydrocarbon liquid extrusion aid is an isoalkane solvent oil, whose main components are C11-C14 isoalkanes, with a mass content of 98.5% for C11-C14 isoalkanes, a mass content of 0.05% for aromatics, a mass content of 0.0005% for sulfur, and a density of 0.755 g / cm³ at 20°C. 3 The initial boiling point is 180℃, the final boiling point is 285℃, the boiling range is determined according to GB / T 6536, and the kinematic viscosity at 40℃ is 2.4 mm. 2 / s, kinematic viscosity was determined according to GB / T 265, flash point was 72℃, and flash point was determined according to GB / T 261.

[0062] The preparation method of this embodiment includes the following steps.

[0063] S1: Add 6 parts of perfluoroalkoxy resin, 3.6 parts of polyimide micro powder and 35 parts of polytetrafluoroethylene resin with the first particle size to a horizontal low-shear mixer. First, premix at 80 r / min for 3 min, then mix at 120 r / min for 13 min. During the mixing process, control the material temperature at 22℃. After the mixing is completed, pass the mixture through a 20-mesh sieve to remove obvious agglomerated particles and obtain pre-dispersed powder.

[0064] S2: Add 65 parts of second-size polytetrafluoroethylene resin, 9.5 parts of needle-shaped calcium silicate treated with fluorinated silane layer and 0.9 parts of fluorinated graphite to the pre-dispersed powder obtained in S1. Mix at 70 r / min for 5 min and then at 100 r / min for 12 min. Control the material temperature not to exceed 28℃ during the mixing process to obtain composite powder.

[0065] S3: Add 23 parts of hydrocarbon liquid extrusion aid to the composite powder obtained in S2 by atomization spraying. During the spraying process, the composite powder is continuously turned at 60 r / min for 18 min. After the spraying is completed, continue mixing at 60 r / min for 8 min to allow the hydrocarbon liquid extrusion aid to penetrate into the gaps between the composite powder particles. Then, put the moistened powder into a sealed polyethylene container and let it stand at 25°C for 18 h to obtain the moistened powder.

[0066] S4: The wet powder obtained in S3 is loaded into the tube blank mold for the first cold pressing. The inner core diameter of the tube blank mold is 40mm, the inner diameter of the outer mold is 55mm, and the effective forming length is 220mm. The wet powder is added in 3 batches, and after each addition, it is gently vibrated for 10s to ensure that the wet powder is evenly spread in the mold cavity. After loading, the first cold pressing is performed. The first cold pressing pressure is 24MPa, the pressure increase rate is 3MPa / min, and after reaching 24MPa, the pressure is held for 5min. After depressurization, a first compact is obtained. The first compact is left to stand at 25℃ for 25min, and then a second cold pressing is performed. The second cold pressing pressure is 32MPa, the pressure increase rate is 3MPa / min, and after reaching 32MPa, the pressure is held for 8min. After depressurization, a second compact is obtained.

[0067] In this embodiment, the relative density of the solid skeleton is used to evaluate the geometric retention state of the solid skeleton in the tube blank during cold pressing, depressurization and settling, and extrusion agent removal. The relative density of the solid skeleton is calculated using the following formula: The relative density of a solid skeleton is D = V0 / V; In the formula, D represents the relative density of the solid skeleton, V0 represents the theoretical volume of the solid components after removing the hydrocarbon liquid extrusion aids, and V represents the measured geometric volume of the compact or tube blank. The theoretical volume V0 of the solid components is calculated by summing the ratios of the mass of each solid component to its true density. The measured geometric volume V of the compact or tube blank is calculated based on the measured values ​​of its outer diameter, inner diameter, and length. For primary compacts, secondary compacts, and de-agent tube blanks, the theoretical volume V0 of the solid components after removing the hydrocarbon liquid extrusion aids is used as the unified calculation benchmark.

[0068] In this embodiment, the actual density of the polytetrafluoroethylene resin with the first particle size is 2.17 g / cm³. 3 The actual density of the second-sized polytetrafluoroethylene resin is 2.18 g / cm³. 3 The actual density of the perfluoroalkoxy resin is 2.15 g / cm³. 3 The actual density of polyimide micro powder is 1.42 g / cm³. 3 The actual density of needle-shaped calcium silicate is 2.90 g / cm³. 3 The actual density of fluorinated graphite is 2.20 g / cm³. 3 The actual density was measured using a helium true density meter. Calculations show that the theoretical volume V0 of the solid component after removing the hydrocarbon liquid extrusion aid in this embodiment is 54.98 cm³. 3 .

[0069] The rate of decrease in the relative density of the solid skeleton of the primary blank after the first cold pressing and subsequent resting is denoted as R1, where R1 = (D1 - D2) / D1 × 100%, and D1 is the relative density of the solid skeleton of the primary blank measured immediately after the first cold pressing and D2 is the relative density of the solid skeleton measured after the primary blank has been rested. In this embodiment, the outer diameter, inner diameter, and length of the primary blank are measured immediately after the first cold pressing and its geometric volume is calculated, resulting in D1 of 0.505. After the primary blank is rested at 25°C for 25 minutes, its outer diameter, inner diameter, and length are measured again and its geometric volume is calculated, resulting in D2 of 0.487. Therefore, R1 is calculated to be 3.56%.

[0070] S5: The secondary pressed blank obtained in S4 is placed in a hot air circulating oven for de-extrusion agent treatment. First, it is kept at 80℃ for 60 min, then the temperature is raised to 130℃ and kept for 90 min, and then the temperature is raised to 180℃ and kept for 150 min. The heating rate is 1.5℃ / min. The oven exhaust is kept on during the de-extrusion agent treatment. After the de-extrusion agent treatment is completed, it is naturally cooled to below 60℃ in the oven and then taken out to obtain the de-extrusion agent tube blank.

[0071] The relative density reduction rate of the solid skeleton of the secondary compact after the second cold pressing and the treatment of the extrusion aid removal agent is denoted as R2. R2 = (D3 - D4) / D3 × 100%, where D3 is the relative density of the solid skeleton of the secondary compact immediately after the second cold pressing and the pressure is released, and D4 is the relative density of the solid skeleton of the extrusion aid removal agent-free tube blank obtained after the treatment of the secondary compact and the extrusion aid removal agent. In this embodiment, the outer diameter, inner diameter, and length of the secondary compact are measured immediately after the pressure is released from the second cold pressing and its geometric volume is calculated, resulting in D3 of 0.552; the outer diameter, inner diameter, and length of the extrusion aid removal agent-free tube blank are measured after the treatment of the secondary compact and its geometric volume is calculated, resulting in D4 of 0.543; thus, R2 is calculated to be 1.63%, and R1 / R2 is 2.18.

[0072] S6: The de-agent tube blank obtained in S5 is placed in a sintering furnace for sintering and shaping. The temperature is raised from room temperature to 315℃ and pre-sintered at 315℃ for 35 min. The temperature is then raised to 375℃ and main sintered at 375℃ for 65 min. The temperature is then lowered to 358℃ and held at 358℃ for 40 min. After the holding period, the tube blank is cooled in stages for shaping. The average cooling rate from 375℃ to 260℃ is controlled at 1.5℃ / min, and the average cooling rate from 260℃ to 180℃ is controlled at 0.8℃ / min. After cooling to 180℃, the tube blank is cooled to below 60℃ in the furnace. After removal, a polytetrafluoroethylene tube with high impact resistance is obtained. Example 2

[0073] This embodiment discloses a polytetrafluoroethylene pipe with high impact resistance, which differs from Embodiment 1 only in the formulation and some process parameters.

[0074] The raw materials for preparation, by weight, include the following components: 100 parts of polytetrafluoroethylene resin, 4.5 parts of perfluoroalkoxy resin, 2.8 parts of polyimide micro powder, 7.5 parts of needle-shaped calcium silicate, 0.7 parts of fluorinated graphite, and 21 parts of hydrocarbon liquid extrusion aid.

[0075] The average particle size of the first-size PTFE resin is 28 μm, and the dosage is 32 parts; the average particle size of the second-size PTFE resin is 55 μm, and the dosage is 68 parts; the mass ratio of the first-size to the second-size PTFE resin is 1:2.13. The average particle size of the perfluoroalkoxy resin is 10 μm. The average particle size (D50) of the polyimide micropowder is 3 μm, and the average particle size (D90) is 6 μm. The average particle size (D50) of the fluorinated graphite is 4 μm. The average length of the needle-shaped calcium silicate is 12 μm, the average diameter is 1.0 μm, the aspect ratio is 12, and the contact angle after treatment is 100°.

[0076] In this embodiment, the mass ratio of perfluoroalkoxy resin to polyimide micropowder is 1.61:1, the mass ratio of polyimide micropowder to needle-shaped calcium silicate is 1:2.68, and the mass ratio of fluorinated graphite to needle-shaped calcium silicate is 1:10.71. The ratio of the average particle size of the perfluoroalkoxy resin to the average particle size D50 of the polyimide micropowder is 3.33:1, the ratio of the average particle size D50 of the fluorinated graphite to the average particle size D50 of the polyimide micropowder is 1.33:1, and the ratio of the average length of the needle-shaped calcium silicate to the average particle size of the perfluoroalkoxy resin is 1.20:1.

[0077] The preparation method of this embodiment includes the following steps.

[0078] S1: Add 4.5 parts of perfluoroalkoxy resin, 2.8 parts of polyimide micro powder and 32 parts of polytetrafluoroethylene resin with the first particle size to a horizontal low-shear mixer. First, premix at 80 r / min for 3 min, then mix at 100 r / min for 12 min. During the mixing process, control the material temperature at 22℃. After the mixing is completed, pass the mixture through a 20-mesh sieve to obtain pre-dispersed powder.

[0079] S2: Add 68 parts of second-size polytetrafluoroethylene resin, 7.5 parts of needle-shaped calcium silicate treated with fluorinated silane layer and 0.7 parts of fluorinated graphite to the pre-dispersed powder obtained in S1. Mix at 70 r / min for 5 min and then at 90 r / min for 12 min. Control the material temperature not to exceed 28℃ during the mixing process to obtain composite powder.

[0080] S3: Add 21 parts of hydrocarbon liquid extrusion aid to the composite powder obtained in S2 by atomization spraying. During the spraying process, the composite powder is continuously turned at 60 r / min for 18 min. After the spraying is completed, continue mixing at 60 r / min for 8 min. Then, put the moistened powder into a sealed polyethylene container and let it stand at 25°C for 18 h to obtain the moistened powder.

[0081] S4: The wet powder obtained in S3 is loaded into the tube blank mold for the first cold pressing. The first cold pressing pressure is 20MPa, the pressure increase rate is 3MPa / min, and after reaching 20MPa, the pressure is held for 4min. After depressurization, a first-pressed blank is obtained. The first-pressed blank is left to stand at 25℃ for 15min, and then a second cold pressing is performed. The second cold pressing pressure is 26MPa, the pressure increase rate is 3MPa / min, and after reaching 26MPa, the pressure is held for 6min. After depressurization, a second-pressed blank is obtained.

[0082] S5: The secondary pressed blank obtained in S4 is placed in a hot air circulating oven for de-extrusion agent treatment. First, it is kept at 80℃ for 60 min, then the temperature is raised to 130℃ and kept for 90 min, and then the temperature is raised to 180℃ and kept for 150 min. The heating rate is 1.5℃ / min. The oven exhaust is kept on during the de-extrusion agent treatment. After the de-extrusion agent treatment is completed, it is naturally cooled to below 60℃ in the oven and then taken out to obtain the de-extrusion agent tube blank.

[0083] S6: The de-agent tube blank obtained in S5 is placed in a sintering furnace for sintering and shaping. The temperature is raised from room temperature to 310℃ and pre-sintered at 310℃ for 30 min. The temperature is then raised to 370℃ and main sintered at 370℃ for 55 min. The temperature is then lowered to 355℃ and held at 355℃ for 30 min. After the holding period, the tube blank is cooled in stages for shaping. The average cooling rate from 370℃ to 260℃ is controlled at 1.8℃ / min, and the average cooling rate from 260℃ to 180℃ is controlled at 1.0℃ / min. After cooling to 180℃, the tube blank is cooled to below 60℃ in the furnace and then removed to obtain polytetrafluoroethylene (PTFE) tube.

[0084] In this embodiment, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.492. After standing for 15 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.480. The relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was reduced by 2.44%.

[0085] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.538. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.532. The relative density reduction rate of the solid skeleton of the secondary compact after the second cold pressing and extrusion aid removal treatment was 1.12%, and the ratio of R1 to R2 was 2.18. Example 3

[0086] This embodiment discloses a polytetrafluoroethylene pipe with high impact resistance, which differs from Embodiment 1 only in the formulation and some process parameters.

[0087] The raw materials for preparation, by weight, include the following components: 100 parts of polytetrafluoroethylene resin, 7.5 parts of perfluoroalkoxy resin, 5.0 parts of polyimide micro powder, 12 parts of needle-shaped calcium silicate, 1.2 parts of fluorinated graphite, and 25 parts of hydrocarbon liquid extrusion aid.

[0088] The average particle size of the first-size PTFE resin is 42 μm, and the dosage is 40 parts; the average particle size of the second-size PTFE resin is 70 μm, and the dosage is 60 parts; the mass ratio of the first-size PTFE resin to the second-size PTFE resin is 1:1.50. The average particle size of the perfluoroalkoxy resin is 22 μm. The average particle size (D50) of the polyimide micropowder is 5 μm, and the average particle size (D90) is 10 μm. The average particle size (D50) of the fluorinated graphite is 8 μm. The average length of the needle-shaped calcium silicate is 25 μm, the average diameter is 1.8 μm, the aspect ratio is 13.9, and the contact angle after treatment is 120°.

[0089] In this embodiment, the mass ratio of perfluoroalkoxy resin to polyimide micropowder is 1.50:1, the mass ratio of polyimide micropowder to needle-shaped calcium silicate is 1:2.40, and the mass ratio of fluorinated graphite to needle-shaped calcium silicate is 1:10. The ratio of the average particle size of the perfluoroalkoxy resin to the average particle size D50 of the polyimide micropowder is 4.40:1, the ratio of the average particle size D50 of the fluorinated graphite to the average particle size D50 of the polyimide micropowder is 1.60:1, and the ratio of the average length of the needle-shaped calcium silicate to the average particle size of the perfluoroalkoxy resin is 1.14:1.

[0090] The preparation method of this embodiment includes the following steps.

[0091] S1: Add 7.5 parts of perfluoroalkoxy resin, 5.0 parts of polyimide micro powder and 40 parts of polytetrafluoroethylene resin with the first particle size to a horizontal low-shear mixer. First, premix at 90 r / min for 3 min, then mix at 150 r / min for 15 min. During the mixing process, control the material temperature at 24℃. After the mixing is completed, pass the mixture through a 20-mesh sieve to obtain pre-dispersed powder.

[0092] S2: Add 60 parts of second-size polytetrafluoroethylene resin, 12 parts of needle-shaped calcium silicate treated with fluorinated silane layer and 1.2 parts of fluorinated graphite to the pre-dispersed powder obtained in S1. Mix at 80 r / min for 5 min and then at 110 r / min for 12 min. Control the material temperature not to exceed 28℃ during the mixing process to obtain composite powder.

[0093] S3: Add 25 parts of hydrocarbon liquid extrusion aid to the composite powder obtained in S2 by atomization spraying. During the spraying process, the composite powder is continuously turned at 60 r / min for 20 min. After the spraying is completed, continue mixing at 60 r / min for 10 min. Then, put the moistened powder into a sealed polyethylene container and let it stand at 25°C for 20 h to obtain the moistened powder.

[0094] S4: The wet powder obtained in S3 is loaded into the tube blank mold for the first cold pressing. The first cold pressing pressure is 27MPa, the pressure increase rate is 3MPa / min, and after reaching 27MPa, the pressure is held for 7min. After depressurization, a first-pressed blank is obtained. The first-pressed blank is left to stand at 25℃ for 32min, and then a second cold pressing is performed. The second cold pressing pressure is 36MPa, the pressure increase rate is 3MPa / min, and after reaching 36MPa, the pressure is held for 10min. After depressurization, a second-pressed blank is obtained.

[0095] S5: The secondary pressed blank obtained in S4 is placed in a hot air circulating oven for de-extrusion agent treatment. First, it is kept at 80℃ for 70 min, then the temperature is raised to 135℃ and kept for 100 min, and then the temperature is raised to 180℃ and kept for 160 min. The heating rate is 1.3℃ / min. The oven exhaust is kept on during the de-extrusion agent treatment. After the de-extrusion agent treatment is completed, it is naturally cooled to below 60℃ in the oven and then taken out to obtain the de-extrusion agent tube blank.

[0096] S6: The de-agent tube blank obtained in S5 is placed in a sintering furnace for sintering and shaping. The temperature is raised from room temperature to 322℃ and pre-sintered at 322℃ for 42 min. The temperature is then raised to 380℃ and main sintered at 380℃ for 78 min. The temperature is then lowered to 363℃ and held at 363℃ for 50 min. After the holding period, the tube blank is cooled in stages for shaping. The average cooling rate from 380℃ to 260℃ is controlled at 1.0℃ / min, and the average cooling rate from 260℃ to 180℃ is controlled at 0.6℃ / min. After cooling to 180℃, the tube blank is cooled to below 60℃ in the furnace and then removed to obtain polytetrafluoroethylene (PTFE) tube.

[0097] In this embodiment, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.516. After standing for 32 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.490. The relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was reduced by 5.04%.

[0098] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.565. After the removal of the extrusion aid, the relative density of the solid skeleton of the de-extrusion aid tube was measured to be 0.555. The relative density reduction rate of the solid skeleton of the secondary compact after the second cold pressing and the removal of the extrusion aid was 1.77%, and the ratio of R1 to R2 was 2.85. Example 4

[0099] This embodiment discloses a polytetrafluoroethylene pipe with high impact resistance. The only difference from Example 1 is the ratio of perfluoroalkoxy resin to polyimide micro powder.

[0100] By weight, the perfluoroalkoxy resin comprises 5.2 parts, polyimide micropowder 4.2 parts, acicular calcium silicate 9.5 parts, and fluorinated graphite 0.9 parts. The amounts of polytetrafluoroethylene resin and hydrocarbon liquid extrusion aid are the same as in Example 1. The mass ratio of perfluoroalkoxy resin to polyimide micropowder is 1.24:1, the mass ratio of polyimide micropowder to acicular calcium silicate is 1:2.26, and the mass ratio of fluorinated graphite to acicular calcium silicate is 1:10.56.

[0101] In the preparation method, S1: 5.2 parts of perfluoroalkoxy resin, 4.2 parts of polyimide micro powder, and 35 parts of polytetrafluoroethylene resin with the first particle size are added to a horizontal low-shear mixer. The mixture is pre-mixed at 80 r / min for 3 min, then mixed at 120 r / min for 13 min to obtain a pre-dispersed powder. S2: 65 parts of polytetrafluoroethylene resin with the second particle size, 9.5 parts of needle-shaped calcium silicate treated with a fluorinated silane layer, and 0.9 parts of fluorinated graphite are added to the pre-dispersed powder obtained in S1, and the composite powder is obtained according to the mixing method of Example 1. S3 to S6 are the same as in Example 1.

[0102] In this embodiment, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.503. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.487. The relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was reduced by 3.18%.

[0103] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.550. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.542. The relative density reduction rate of the solid skeleton of the secondary compact after the second cold pressing and extrusion aid removal treatment was 1.45%, and the ratio of R1 to R2 was 2.19. Example 5

[0104] This embodiment discloses a polytetrafluoroethylene pipe with high impact resistance. The only difference from Example 1 is the ratio of polyimide micro powder to needle-shaped calcium silicate.

[0105] By weight, the perfluoroalkoxy resin comprises 6 parts, polyimide micropowder 4.8 parts, acicular calcium silicate 10.5 parts, fluorinated graphite 1.0 part, and the amounts of polytetrafluoroethylene resin and hydrocarbon liquid extrusion aid are the same as in Example 1. The mass ratio of perfluoroalkoxy resin to polyimide micropowder is 1.25:1, the mass ratio of polyimide micropowder to acicular calcium silicate is 1:2.19, and the mass ratio of fluorinated graphite to acicular calcium silicate is 1:10.50.

[0106] In the preparation method, S1: 6 parts of perfluoroalkoxy resin, 4.8 parts of polyimide micro powder, and 35 parts of polytetrafluoroethylene resin with a first particle size are added to a horizontal low-shear mixer, and a pre-dispersed powder is obtained according to the mixing method of Example 1. S2: 65 parts of polytetrafluoroethylene resin with a second particle size, 10.5 parts of needle-shaped calcium silicate treated with a fluorinated silane layer, and 1.0 part of fluorinated graphite are added to the pre-dispersed powder obtained in S1, and a composite powder is obtained according to the mixing method of Example 1. S3 to S6 are the same as in Example 1.

[0107] In this embodiment, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.512. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.492. The relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was reduced by 3.91%.

[0108] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.556. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.548. The relative density reduction rate of the solid skeleton of the secondary compact after the second cold pressing and extrusion aid removal treatment was 1.44%, and the ratio of R1 to R2 was 2.72. Example 6

[0109] This embodiment discloses a polytetrafluoroethylene pipe with high impact resistance. The only difference from Embodiment 1 is the ratio of fluorinated graphite to needle-shaped calcium silicate.

[0110] By weight, the perfluoroalkoxy resin comprises 6 parts, polyimide micropowder 3.6 parts, acicular calcium silicate 10.5 parts, and fluorinated graphite 1.5 parts. The amounts of polytetrafluoroethylene resin and hydrocarbon liquid extrusion aid are the same as in Example 1. The mass ratio of perfluoroalkoxy resin to polyimide micropowder is 1.67:1, the mass ratio of polyimide micropowder to acicular calcium silicate is 1:2.92, and the mass ratio of fluorinated graphite to acicular calcium silicate is 1:7.00.

[0111] In the preparation method, S1 is the same as in Example 1. S2: 65 parts of second-size polytetrafluoroethylene resin, 10.5 parts of needle-shaped calcium silicate treated with a fluorinated silane layer, and 1.5 parts of fluorinated graphite are added to the pre-dispersed powder obtained in S1, and the composite powder is obtained by mixing in the manner of Example 1. S3 to S6 are the same as in Example 1.

[0112] In this embodiment, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.518. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.497. The relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was reduced by 4.05%.

[0113] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.554. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.544. The rate of decrease in the relative density of the solid skeleton of the secondary compact after the second cold pressing and the removal of the extrusion aid was R2, which was 1.81%, and the ratio of R1 to R2 was 2.24. Example 7

[0114] This embodiment discloses a polytetrafluoroethylene pipe with high impact resistance. The only difference from Embodiment 1 is the scale ratio of the length of the needle-shaped calcium silicate to the particle size of the perfluoroalkoxy resin.

[0115] The perfluoroalkoxy resin has an average particle size of 20 μm, the needle-like calcium silicate has an average length of 26 μm, an average diameter of 1.6 μm, and an aspect ratio of 16.25. The ratio of the average length of the needle-like calcium silicate to the average particle size of the perfluoroalkoxy resin is 1.30:1. The amounts and specifications of the remaining raw materials are the same as in Example 1.

[0116] In the preparation method, S1 to S6 are the same as in Example 1.

[0117] In this embodiment, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.506. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.489. The relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was reduced by 3.36%.

[0118] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.559. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.551. The relative density reduction rate of the solid skeleton of the secondary compact after the removal of the extrusion aid after the second cold pressing was 1.43%, and the ratio of R1 to R2 was 2.35. Example 8

[0119] This embodiment discloses a polytetrafluoroethylene (PTFE) pipe with high impact resistance. The only difference from Embodiment 1 is the proportion of PTFE resin and the pre-dispersion conditions in the first part.

[0120] The amount of PTFE resin with the first particle size is 40 parts, and the amount of PTFE resin with the second particle size is 60 parts. The PTFE resin with the first particle size accounts for 40% of the total mass of PTFE resin, and the mass ratio of the PTFE resin with the first particle size to the PTFE resin with the second particle size is 1:1.50. The amounts of other raw materials are the same as in Example 1.

[0121] The preparation method of this embodiment includes the following steps.

[0122] S1: Add 6 parts of perfluoroalkoxy resin, 3.6 parts of polyimide micro powder and 40 parts of polytetrafluoroethylene resin with the first particle size to a horizontal low-shear mixer. First, premix at 90 r / min for 3 min, then mix at 150 r / min for 15 min. During the mixing process, control the material temperature at 22℃. After the mixing is completed, pass the mixture through a 20-mesh sieve to obtain pre-dispersed powder.

[0123] S2: 60 parts of second-size polytetrafluoroethylene resin, 9.5 parts of needle-shaped calcium silicate treated with fluorinated silane layer and 0.9 parts of fluorinated graphite are added to the pre-dispersed powder obtained in S1, and the composite powder is obtained by mixing in the manner described in Example 1.

[0124] S3 to S6 are the same as in Example 1.

[0125] In this embodiment, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.507. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.488. The relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was reduced by 3.75%.

[0126] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.555. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.546. The relative density reduction rate of the solid skeleton of the secondary compact after the removal of the extrusion aid after the second cold pressing was 1.62%, and the ratio of R1 to R2 was 2.31. Example 9

[0127] This embodiment discloses a polytetrafluoroethylene pipe with high impact resistance. The only difference from Embodiment 1 is the difference in the two cold pressing parameters and the pressure relief and standing time.

[0128] The formulation and S1 to S3 are the same as in Example 1.

[0129] S4: The wet powder obtained in S3 is loaded into the tube blank mold for the first cold pressing. The first cold pressing pressure is 26MPa, the pressure increase rate is 3MPa / min, and after reaching 26MPa, the pressure is held for 7min. After depressurization, a first-pressed blank is obtained. The first-pressed blank is placed at 25℃ for 30min, and then subjected to a second cold pressing. The second cold pressing pressure is 36MPa, the pressure increase rate is 3MPa / min, and after reaching 36MPa, the pressure is held for 10min. After depressurization, a second-pressed blank is obtained.

[0130] S5 and S6 are the same as in Example 1.

[0131] The relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the result was 0.522. After standing for 30 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.499. The rate of decrease in the relative density of the solid skeleton of the first compact after the first cold pressing was 4.41% after depressurization and standing.

[0132] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.568. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.559. The rate of decrease in the relative density of the solid skeleton of the secondary compact after the second cold pressing and the removal of the extrusion aid was R2, which was 1.58%, and the ratio of R1 to R2 was 2.79. Example 10

[0133] This embodiment discloses a polytetrafluoroethylene pipe with high impact resistance. The only difference between this embodiment and Embodiment 1 is the sintering and segmented cooling conditions.

[0134] The formulation and S1 to S5 are the same as in Example 1.

[0135] S6: The de-agent tube blank obtained in S5 is placed in a sintering furnace for sintering and shaping. The temperature is raised from room temperature to 320℃ and pre-sintered at 320℃ for 40 min. The temperature is then raised to 378℃ and main sintered at 378℃ for 75 min. The temperature is then lowered to 362℃ and held at 362℃ for 50 min. After the holding period, the tube blank is cooled in stages for shaping. The average cooling rate from 378℃ to 260℃ is controlled at 1.0℃ / min, and the average cooling rate from 260℃ to 180℃ is controlled at 0.6℃ / min. After cooling to 180℃, the tube blank is cooled to below 60℃ in the furnace and then removed to obtain polytetrafluoroethylene (PTFE) tube.

[0136] In this embodiment, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.505. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.487. The relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was reduced by 3.56%.

[0137] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.556. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.547. The relative density reduction rate of the solid skeleton of the secondary compact after the removal of the extrusion aid after the second cold pressing was 1.62%, and the ratio of R1 to R2 was 2.20.

[0138] Comparative Example 1 This comparative example discloses a polytetrafluoroethylene pipe, which differs from Example 1 only in that it does not contain perfluoroalkoxy resin.

[0139] The raw materials, by weight, comprise the following components: 100 parts polytetrafluoroethylene resin, 3.6 parts polyimide micropowder, 9.5 parts needle-shaped calcium silicate, 0.9 parts fluorinated graphite, and 23 parts hydrocarbon liquid extrusion aid. In the preparation method, S1: 3.6 parts polyimide micropowder and 35 parts of polytetrafluoroethylene resin with the first particle size are added to a horizontal low-shear mixer, pre-mixed at 80 r / min for 3 min, and then mixed at 120 r / min for 13 min to obtain a pre-dispersed powder. S2: 65 parts of polytetrafluoroethylene resin with the second particle size, 9.5 parts of needle-shaped calcium silicate treated with a fluorinated silane layer, and 0.9 parts of fluorinated graphite are added to the pre-dispersed powder obtained in S1, and the composite powder is obtained according to the mixing method of Example 1. S3 to S6 are the same as in Example 1.

[0140] In this comparative example, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.514. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.492. The rate of decline of the relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was 4.28%.

[0141] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.534. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.519. The rate of decrease in the relative density of the solid skeleton of the secondary compact after the second cold pressing and extrusion aid removal treatment was R2, which was 2.81%, and the ratio of R1 to R2 was 1.52.

[0142] Comparative Example 2 This comparative example discloses a polytetrafluoroethylene pipe, which differs from Example 1 only in that it does not contain polyimide micropowder.

[0143] The raw materials, by weight, include the following components: 100 parts polytetrafluoroethylene resin, 6 parts perfluoroalkoxy resin, 9.5 parts needle-shaped calcium silicate, 0.9 parts fluorinated graphite, and 23 parts hydrocarbon liquid extrusion aid. In the preparation method, S1: 6 parts perfluoroalkoxy resin and 35 parts of first-size polytetrafluoroethylene resin are added to a horizontal low-shear mixer, pre-mixed at 80 r / min for 3 min, and then mixed at 120 r / min for 13 min to obtain a pre-dispersed powder. S2: 65 parts of second-size polytetrafluoroethylene resin, 9.5 parts needle-shaped calcium silicate treated with a fluorinated silane layer, and 0.9 parts fluorinated graphite are added to the pre-dispersed powder obtained in S1, and the composite powder is obtained according to the mixing method of Example 1. S3 to S6 are the same as in Example 1.

[0144] In this comparative example, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.508. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.487. The rate of decline of the relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was 4.13%.

[0145] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.542. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.528. The rate of decrease in the relative density of the solid skeleton of the secondary compact after the second cold pressing and the removal of the extrusion aid was R2, which was 2.58%, and the ratio of R1 to R2 was 1.60.

[0146] Comparative Example 3 This comparative example discloses a polytetrafluoroethylene (PTFE) pipe, which differs from Example 1 only in that it does not contain fluorinated graphite.

[0147] The raw materials, by weight, comprise the following components: 100 parts polytetrafluoroethylene resin, 6 parts perfluoroalkoxy resin, 3.6 parts polyimide micropowder, 9.5 parts needle-shaped calcium silicate, and 23 parts hydrocarbon liquid extrusion aid. In the preparation method, S1 is the same as in Example 1. S2: 65 parts of the second-size polytetrafluoroethylene resin and 9.5 parts of needle-shaped calcium silicate treated with a fluorinated silane layer are added to the pre-dispersed powder obtained in S1, and the composite powder is obtained by mixing in the manner described in Example 1. S3 to S6 are the same as in Example 1.

[0148] In this comparative example, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.506. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.486. The rate of decline of the relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was 3.95%.

[0149] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.544. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.531. The relative density reduction rate of the solid skeleton of the secondary compact after the removal of the extrusion aid after the second cold pressing was 2.39%, and the ratio of R1 to R2 was 1.65.

[0150] Comparative Example 4 This comparative example discloses a polytetrafluoroethylene pipe, which differs from Example 1 only in the mass ratio of fluorinated graphite to needle-shaped calcium silicate.

[0151] By weight, the raw materials used in the preparation consist of 2.2 parts of fluorinated graphite and 9.5 parts of needle-shaped calcium silicate, with a mass ratio of fluorinated graphite to needle-shaped calcium silicate of 1:4.32; the amounts of other raw materials are the same as in Example 1.

[0152] In the preparation method, S1 is the same as in Example 1. S2: 65 parts of second-size polytetrafluoroethylene resin, 9.5 parts of needle-shaped calcium silicate treated with a fluorinated silane layer, and 2.2 parts of fluorinated graphite are added to the pre-dispersed powder obtained in S1, and the composite powder is obtained by mixing in the manner of Example 1. S3 to S6 are the same as in Example 1.

[0153] In this comparative example, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.522. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.491. The rate of decline of the relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was 5.94%.

[0154] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.536. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.514. The rate of decrease in the relative density of the solid skeleton of the secondary compact after the second cold pressing and the removal of the extrusion aid was R2, which was 4.10%, and the ratio of R1 to R2 was 1.45.

[0155] Comparative Example 5 This comparative example discloses a polytetrafluoroethylene pipe, which differs from Example 1 only in the amount of perfluoroalkoxy resin and polyimide micro powder used.

[0156] By weight, the perfluoroalkoxy resin is 4.0 parts, the polyimide micro powder is 2.0 parts, the needle-shaped calcium silicate is still 9.5 parts, and the amounts of polytetrafluoroethylene resin, fluorinated graphite and hydrocarbon liquid extrusion aid are the same as in Example 1.

[0157] In the preparation method, S1 is adjusted as follows: 4.0 parts of perfluoroalkoxy resin, 2.0 parts of polyimide micro powder and 35 parts of polytetrafluoroethylene resin with the first particle size are added to a horizontal low-shear mixer. First, it is premixed at 80 r / min for 3 min, and then mixed at 120 r / min for 13 min. During the mixing process, the material temperature is controlled at 22℃. After the mixing is completed, the mixture is passed through a 20-mesh sieve to remove obvious agglomerated particles and obtain pre-dispersed powder.

[0158] S2 to S6 are the same as in Example 1.

[0159] In this comparative example, the relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the relative density of the solid skeleton of the first compact was measured to be 0.509. After standing for 25 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.485. The rate of decline of the relative density of the solid skeleton of the first compact after the first cold pressing was depressurized and left to stand was 4.72%.

[0160] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.536. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.519. The relative density reduction rate of the solid skeleton of the secondary compact after the removal of the extrusion aid after the second cold pressing was 3.17%, and the ratio of R1 to R2 was 1.49.

[0161] Comparative Example 6 This comparative example discloses a polytetrafluoroethylene pipe, which differs from Example 1 only in that the pressure relief and static setting and the second cold pressing are omitted.

[0162] The formulation, S1, S2 and S3 are the same as in Example 1.

[0163] S4: The wet powder obtained in S3 is loaded into the tube blank mold for cold pressing. The inner core diameter of the tube blank mold is 40mm, the inner diameter of the outer mold is 55mm, and the effective forming length is 220mm. The wet powder is added in 3 batches during loading, and the tube blank is gently vibrated for 10s after each addition. After loading, a cold pressing is performed. The cold pressing pressure is 32MPa, the pressure increase rate is 3MPa / min, and the pressure is held for 8min after reaching 32MPa. After depressurization, the pressed blank is obtained.

[0164] S5: The pressed blank obtained in S4 is placed in a hot air circulating oven for de-extrusion agent treatment. The treatment conditions are the same as in Example 1, and a de-extrusion agent tube blank is obtained.

[0165] S6 is the same as in Example 1.

[0166] This comparative example did not undergo a second cold pressing after depressurization and settling. Therefore, it did not establish the relative density reduction rate R1 of the solid skeleton produced by the first cold pressing and settling after depressurization, nor did it establish the multiple relationship between R1 and the relative density reduction rate R2 of the solid skeleton produced by the second cold pressing and settling after the removal of extrusion aid.

[0167] In this comparative example, the relative density of the solid skeleton of the compact was measured immediately after depressurization in the cold-pressed form (D3') to be 0.541. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.517. The reduction rate of the relative density of the solid skeleton of the compact after the removal of the extrusion aid was 4.44%. This result indicates that after eliminating the depressurization and static setting and the second cold-pressing, the solid skeleton retention capacity of the compact decreased during the removal of the extrusion aid, and the geometric reduction during the removal stage increased.

[0168] Comparative Example 7 This comparative example discloses a polytetrafluoroethylene pipe, which differs from Example 1 only in that it retains the two cold pressing molding processes, but controls the ratio of the first solid skeleton relative density reduction rate to the second solid skeleton relative density reduction rate to be less than 2.

[0169] The formulation, S1, S2 and S3 are the same as in Example 1.

[0170] S4: The wet powder obtained in S3 is loaded into the tube blank mold for the first cold pressing. The first cold pressing pressure is 24MPa, the pressure increase rate is 3MPa / min, and after reaching 24MPa, the pressure is held for 5min. After depressurization, a first-pressed blank is obtained. The first-pressed blank is left to stand at 25℃ for 8min, and then a second cold pressing is performed. The second cold pressing pressure is 32MPa, the pressure increase rate is 3MPa / min, and after reaching 32MPa, the pressure is held for 8min. After depressurization, a second-pressed blank is obtained.

[0171] S5 and S6 are the same as in Example 1.

[0172] The relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the result was 0.496. After standing for 8 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.484. The rate of decrease in the relative density of the solid skeleton of the first compact after the first cold pressing was 2.42% after depressurization and standing.

[0173] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.546. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.537. The relative density of the solid skeleton of the secondary compact after the removal of the extrusion aid after the second cold pressing was reduced by 1.65% (R2), and the ratio of R1 to R2 was 1.47, which is lower than 2.

[0174] Comparative Example 8 This comparative example discloses a polytetrafluoroethylene pipe, which differs from Example 1 only in that it retains the two cold pressing molding processes, but controls the ratio of the first solid skeleton relative density reduction rate to the second solid skeleton relative density reduction rate to be higher than 4.

[0175] The formulation, S1, S2 and S3 are the same as in Example 1.

[0176] S4: The wet powder obtained in S3 is loaded into the tube blank mold for the first cold pressing. The first cold pressing pressure is 27MPa, the pressure increase rate is 3MPa / min, and after reaching 27MPa, the pressure is held for 7min. After depressurization, a first-pressed blank is obtained. The first-pressed blank is left to stand at 25℃ for 40min, and then a second cold pressing is performed. The second cold pressing pressure is 36MPa, the pressure increase rate is 3MPa / min, and after reaching 36MPa, the pressure is held for 10min. After depressurization, a second-pressed blank is obtained.

[0177] S5 and S6 are the same as in Example 1.

[0178] The relative density of the solid skeleton of the first compact was measured immediately after the first cold pressing was depressurized, and the result was 0.527. After standing for 40 minutes, the relative density of the solid skeleton of the first compact was measured to be 0.497. The rate of decrease in the relative density of the solid skeleton of the first compact after the first cold pressing was 5.69% after depressurization and standing.

[0179] Immediately after the second cold pressing and depressurization, the relative density of the solid skeleton of the secondary compact was measured to be 0.544. After the removal of the extrusion aid, the relative density of the solid skeleton of the extrusion aid-free compact was measured to be 0.538. The rate of decrease in the relative density of the solid skeleton of the secondary compact after the second cold pressing and extrusion aid removal treatment was 1.10%, and the ratio of R1 to R2 was 5.17, which is higher than 4. Performance testing

[0180] To verify the structural integrity, dimensional stability, and impact resistance of the polytetrafluoroethylene (PTFE) pipes prepared according to this invention, performance tests were conducted on the PTFE pipes prepared in Examples 1-10 and Comparative Examples 1-8. Samples for all examples and comparative examples were prepared using the same specification tube blank mold. After sintering, the samples were placed in an environment of 23°C and 50% relative humidity for 24 hours before testing. Twenty-five pipe samples were prepared for each group of samples, and the average value of the test results was taken.

[0181] 1. Inspection of Appearance Integrity and Sintering Cracking Rate: The sintered PTFE pipes of each group were observed under natural light, and the outer wall, inner wall, and end face of the pipes were examined using a 10x magnifying glass for cracks, delamination, collapse, or obvious holes. If a crack longer than 2mm, penetrating delamination, or obvious end face cracking appeared in the same pipe sample, the sample was determined to be a cracked sample. The sintering cracking rate was calculated as the percentage of cracked samples out of the total number of samples in the same group.

[0182] 2. Apparent Density and Dimensional Shrinkage Rate Testing: Take sintered PTFE pipe samples from each group and measure their mass, outer diameter, inner diameter, and length. Calculate the apparent density after sintering based on the pipe's geometric volume. Test 5 samples per group. For each sample, measure the outer and inner diameters at three positions along its length (top, middle, and bottom), and use the average value for calculation. Dimensional shrinkage rate is based on the change between the outer diameter of the pre-sintered blank and the outer diameter of the sintered pipe, calculated as the percentage of the difference between the pre-sintered and post-sintered outer diameters relative to the pre-sintered outer diameter.

[0183] 3. Notched Impact Strength Test of Simply Supported Beam: Strip specimens were cut axially from the walls of each group of PTFE pipes and processed into notched impact specimens. The specimens were 80 mm long, 10 mm wide, and the thickness was processed and trimmed to 4 mm according to the actual pipe wall thickness. The notch depth was 2 mm. Before testing, the specimens were placed in an environment of 23℃ for 24 hours. Ten specimens were tested in each group using a simply supported beam impact testing machine. The impact absorbed energy was recorded and converted into notched impact strength. The average value of the results was taken.

[0184] 4. Drop Hammer Impact Test: Cut each group of PTFE pipes into 100mm long sections. After smoothing both ends, place the sections on a V-shaped support, ensuring the impact point is at the midpoint of the section's length. Use a 1.0kg drop hammer to freely drop from a height of 1.0m onto the outer wall of the pipe. Test 10 sections per group. After impact, observe whether the pipe shows through cracks, end cracks, obvious delamination, or wall breakage. If none of the 10 samples exhibit the above damage, the test is considered passed; if any sample shows the above damage, the test is considered failed.

[0185] The test results are summarized in Table 1.

[0186] Table 1 Test Results Example 1 2.142 12.8 0 24.8 pass Example 2 2.128 13.6 0 22.6 pass Example 3 2.151 14.2 0 23.7 pass Example 4 2.137 13.1 0 24.1 pass Example 5 2.146 12.6 0 25.3 pass Example 6 2.132 13.4 0 23.9 pass Example 7 2.139 12.9 0 24.6 pass Example 8 2.136 13.3 0 24.3 pass Example 9 2.153 12.4 0 25.8 pass Example 10 2.149 11.8 0 25.1 pass Comparative Example 1 2.086 16.8 12 16.9 Not passed Comparative Example 2 2.094 15.9 8 17.8 Not passed Comparative Example 3 2.101 15.3 8 18.4 Not passed Comparative Example 4 2.073 18.5 16 15.6 Not passed Comparative Example 5 2.081 17.9 12 16.4 Not passed Comparative Example 6 2.052 21.4 20 14.7 Not passed Comparative Example 7 2.092 16.3 8 18.1 Not passed Comparative Example 8 2.107 15.7 8 19.3 Not passed The test results show that the PTFE pipes prepared in Examples 1-10 have high apparent density after sintering, which is within a reasonable range. They also exhibit low dimensional shrinkage, no sintering cracking, and maintain a high level of notched impact strength, passing all drop hammer impact tests. This indicates that, through the combined effects of component ratio, particle size ratio, matching of needle-like calcium silicate sizes, and control of the relative density reduction rate of the solid skeleton during two-stage cold pressing, a relatively stable filler embedding structure and continuous stress path are formed inside the pipe, achieving a balance between pipe wall density, dimensional stability, and impact resistance.

[0187] Comparative Example 1, without the addition of perfluoroalkoxy resin, showed a decrease in apparent density and impact strength after sintering, indicating that the lack of fluorinated auxiliary bonding components reduced the interfacial bonding stability between polytetrafluoroethylene particles, polyimide micropowder, and needle-like calcium silicate. Comparative Example 2, without the addition of polyimide micropowder, lacked fine-scale stress transition nodes around the needle-like calcium silicate, making it easier for impact loads to concentrate at the ends and sidewalls of the rigid filler. Comparative Example 3, without the addition of fluorinated graphite, lacked low-shear interface release conditions around the needle-like calcium silicate, making it more prone to localized cracking after impact. Comparative Examples 4 and 5 deviated from the mass ratios of fluorinated graphite to needle-like calcium silicate and polyimide micropowder to needle-like calcium silicate, respectively, indicating that a proper balance needs to be maintained between low-shear release, point stress dispersion, and linear load-bearing capacity. Comparative Example 6, without depressurization and static setting and the second cold pressing, showed a significant increase in sintering cracking rate and dimensional shrinkage rate, indicating that without structural release and re-compaction processes after the first compaction, the tube blank was more prone to abrupt porosity changes and interfacial loosening during the removal of extrusion aids and sintering. Although Comparative Examples 7 and 8 retained two cold pressing cycles, the ratio between the relative density reduction rate of the solid skeleton deviated from the range of 2 to 4, indicating that the ratio between the relative density reduction rate of the solid skeleton in the two stages has an important influence on the process of stress release, structural rearrangement and skeleton maintenance of the tube blank.

[0188] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A polytetrafluoroethylene (PTFE) pipe with high impact resistance, characterized in that, The polytetrafluoroethylene (PTFE) tubing comprises a PTFE resin matrix and perfluoroalkoxy resin, polyimide micro powder, needle-shaped calcium silicate, and fluorinated graphite distributed in the PTFE resin matrix. Based on 100 parts by weight of the polytetrafluoroethylene resin matrix, the perfluoroalkoxy resin comprises 4 to 8 parts by weight, the polyimide micro powder comprises 2.5 to 6 parts by weight, the needle-shaped calcium silicate comprises 7 to 13 parts by weight, and the fluorinated graphite comprises 0.6 to 1.6 parts by weight. The mass ratio of the perfluoroalkoxy resin to the polyimide micro powder is 1.0 to 2.2:1, the mass ratio of the polyimide micro powder to the needle-shaped calcium silicate is 1:1.8 to 3.8, and the mass ratio of the fluorinated graphite to the needle-shaped calcium silicate is 1:6 to 18.

2. The high impact-resistant polytetrafluoroethylene pipe according to claim 1, characterized in that, The polytetrafluoroethylene resin includes a first-size polytetrafluoroethylene resin and a second-size polytetrafluoroethylene resin. The average particle size of the first-size polytetrafluoroethylene resin is 25-45 μm, and the average particle size of the second-size polytetrafluoroethylene resin is 50-75 μm. The mass ratio of the first-size polytetrafluoroethylene resin to the second-size polytetrafluoroethylene resin is 1:1.2-3.

0.

3. The high impact-resistant polytetrafluoroethylene pipe according to claim 2, characterized in that, The average particle size of the perfluoroalkoxy resin is 8–25 μm, the average particle size D50 of the polyimide micro powder is 2–6 μm, and the ratio of the average particle size of the perfluoroalkoxy resin to the average particle size D50 of the polyimide micro powder is 2.0–7.5:1; the average particle size D50 of the fluorinated graphite is 3–9 μm, the ratio of the average particle size D50 of the fluorinated graphite to the average particle size D50 of the polyimide micro powder is 0.8–2.5:1, and the mass ratio of the fluorinated graphite to the needle-shaped calcium silicate is 1:7–16.

4. The high impact-resistant polytetrafluoroethylene pipe according to claim 3, characterized in that, The average length of the needle-shaped calcium silicate is 10–28 μm, the average diameter is 0.6–2.2 μm, and the aspect ratio is 8–20. The ratio of the average length of the needle-shaped calcium silicate to the average particle size of the perfluoroalkoxy resin is 0.7–2.6:

1.

5. The high impact-resistant polytetrafluoroethylene pipe according to claim 4, characterized in that, The surface of the needle-shaped calcium silicate has a fluorinated silane treatment layer, which is formed by hydrolysis and condensation of one of perfluorooctyltriethoxysilane, tridecafluorooctyltriethoxysilane or trifluoropropyltrimethoxysilane. The wetting contact angle of the needle-shaped calcium silicate powder after fluorinated silane treatment is 95° to 125°.

6. A method for preparing a polytetrafluoroethylene pipe with high impact resistance as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Mix perfluoroalkoxy resin, polyimide micro powder and the first part of polytetrafluoroethylene resin to obtain a pre-dispersed powder; S2: Add the second part of polytetrafluoroethylene resin, needle-shaped calcium silicate and fluorinated graphite to the pre-dispersed powder and mix to obtain composite powder; S3: Add the hydrocarbon liquid extrusion aid to the composite powder by spraying, seal and let stand to obtain wet powder; S4: The wet powder is loaded into the tube blank mold for the first cold pressing to obtain the first blank. After the pressure is released and the first blank is allowed to stand, the first blank is cold pressed a second time to obtain the second blank. S5: The secondary pressed billet is subjected to a de-extrusion agent treatment to obtain a de-extrusion agent tube blank; S6: The de-additive tube blank is subjected to pre-sintering, main sintering, heat preservation and cooling shaping in sequence to obtain polytetrafluoroethylene tubes; Using the theoretical volume of the solid components after removing hydrocarbon liquid extrusion aids as a unified calculation benchmark, the relative density of the solid skeleton generated after the first cold pressing and subsequent depressurization and static setting of the primary compact is 2.0%–5.5%; the relative density of the solid skeleton generated after the second cold pressing and subsequent extrusion aid removal of the secondary compact is 1.0%–3.5%. The relative density of the solid skeleton produced after the first cold pressing and subsequent static setting is 2 to 4 times that of the solid skeleton produced after the second cold pressing and subsequent treatment with the extrusion aid removal agent.

7. The method for preparing the high impact-resistant polytetrafluoroethylene pipe according to claim 6, characterized in that, The hydrocarbon liquid extrusion aid is selected from one of isoparaffin solvent oil, naphtha, and white oil. The initial boiling point of the hydrocarbon liquid extrusion aid is 150–220°C, the final boiling point is 230–320°C, and the kinematic viscosity at 40°C is 1.0–5.0 mm. 2 / s.

8. The method for preparing the high impact-resistant polytetrafluoroethylene pipe according to claim 7, characterized in that, In step S1, the first part of polytetrafluoroethylene resin accounts for 28% to 42% of the total mass of polytetrafluoroethylene resin; the perfluoroalkoxy resin, polyimide micro powder and the first part of polytetrafluoroethylene resin are mixed at 80 to 160 r / min for 10 to 16 min.

9. The method for preparing the high impact-resistant polytetrafluoroethylene pipe according to claim 7, characterized in that, In step S4, the pressure of the first cold pressing is 18-28 MPa, and the holding time is 3-8 min; the pressure release and standing time is 12-35 min; the pressure of the second cold pressing is 24-38 MPa, and the holding time is 5-12 min.

10. The method for preparing the high-impact-resistant polytetrafluoroethylene pipe according to claim 7, characterized in that, In step S6, the pre-sintering temperature is 305–325℃ and the pre-sintering time is 25–45 min; the main sintering temperature is 368–382℃ and the main sintering time is 45–85 min; the holding temperature is 352–365℃ and the holding time is 25–55 min; during the cooling and shaping process, the average cooling rate from the main sintering temperature to 260℃ is 0.8–2.2℃ / min, and the average cooling rate from 260℃ to 180℃ is 0.4–1.3℃ / min.